log-warn is a macro. We can arrange it to expand into something suitable.
I am not sure exactly what that would be. In general, when log-warn
is used as shown above, there are a bunch of arbitrary Lisp forms,
and we don't want to have to code-walk them.

What I think we'd want to do is expand the macro such that each of the
forms was wrapped inside a special form meaning "do this, but during
compilation, suppress noting that any variables are being 'used'".

Gail Zacharias says: It might be non-trivial for a somewhat stupid
reason... Currently the warnings come out of real compiler reference
tracking, so you can't really lie - if you don't mark a variable as
referenced in pass1, pass2 won't know to allocate a location for it,
etc. The obvious solution is to add a parallel flag, just for the
warnings, that's usually the same as the real one but can be
manipulated however we want because it's not used by the code
generator. Unfortunately, at first glance it looks to me like we
might be out of bits in the word that holds the per-variable flags,
which probably brings it out of realm of a couple hours into possibly
couple days.